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Air Conditioner BTU Per Square Foot Calculator
The right AC size for any room — accounting for modern insulation.
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The right size matters more than most people think
Oversized AC units cool too quickly without dehumidifying — leaving rooms cold and clammy. Undersized units run constantly without reaching target temperature. The 20 BTU/sq ft rule is a starting point; adjust for ceiling height, sun, and insulation.
Modern insulation changes everything
A well-insulated new home may need 20% fewer BTUs than an older home of the same size. If you've recently added insulation, upgraded windows, or installed weather stripping, factor this in before buying an oversized unit.
⚡ CalcWolf Insight
An oversized AC unit is worse than undersized. It short-cycles, wastes energy, increases wear, and fails to properly dehumidify the air.
Frequently asked questions
How many BTUs do I need per square foot?▾
Standard rule: 20 BTUs per square foot. Adjust up 10–15% for full sun or poor insulation, down 10% for well-shaded modern construction.
How much does it cost to run an AC unit?▾
A standard window unit (8,000 BTU) costs approximately $0.10-0.15/hour or $50-80/month running 8 hours daily. A central AC system (24,000-60,000 BTU) costs $0.20-0.50/hour or $100-300/month. Energy-efficient models (high SEER rating) reduce costs by 20-40%.
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